The present invention relates to a fuel injection apparatus for an internal combustion engine, and more particularly to an apparatus which electrifies injected fuel so as to promote atomization of the fuel into finely divided particles, and to prevent the fuel particles from attaching onto surrounding surfaces, e.g., an inside wall of a suction conduit.
In a conventional electronic controlled fuel injection apparatus for a multi-cylinder engine, a so-called single point injection system (SPI system) utilizes a single fuel injection valve which injects the fuel at a relatively low pressure of about 2 atm, so that injected fuel particles are not finely atomized. Thus, fuel injected from such injection valve tends to attach onto an inside wall of the suction conduit and a outside wall of suction valve, and relatively large portion of the injected fuel flows into the combustion chambers as liquid flow. Since the injected fuel cannot be distributed to each cylinder uniformly, problems occur as to inadequate operational stability, low engine output, starting difficulty at low temperature, and inadequate operational transient response.
To attain finely atomized fuel particles, fuel injection pressure may be increased. However, the fuel pump and fuel injection valve must be elaborated with an accompanying increase of the cost.
A conventional direct injection engine has fuel injection valves each of which injects fuel into each cylinder at high injection pressure, e.g., 100 atm. Fuel injected from such fuel injection valve is atomized into fine particles. However, the injected fuel reaches too far to the walls of cylinder, cylinder head and piston. Fuel attached onto the walls in a liquid state is difficult to perform complete combustion so that combustion efficiency is decreased and incomplete combustion hydrocarbon products tend to increase in the exhaust gas.
It is known that when liquid particles are electrified by high voltage, the particles tend to divide into smaller particles and the electrified particles tend to repulse from a substance of the same polarity. However, a simple and reliable device to electrify fuel particles is not known.